Mechanisms of motor recovery after a stroke remain speculative and available studies using neuroimaging of motored evoked potential techniques have given inconsistent results. We have studies the prognostic value of transcranial magnetic stimulation early have after stroke onset and have defined specific recovery predictive parameters. This project addresses more specifically the mechanisms of cortical plasticity in adult human subjects after stroke. We plan to evaluate changes in the healthy and affected cortex over time in patients recovering from stroke, using transcranial magnetic stimulation (TMS) mapping to determine the relative importance of cortical reorganization in functional recovery, and to correlate this reorganization with motor outcome. This study also evaluates the exact participation of the intact hemisphere in motor recovery after stroke, and assesses changes in interhemispheric inhibition processes between lesioned and normal hemisphere in stroke patients and their influence on motor recovery. We also propose to investigate changes in intrahemispheric inhibition after stroke and to correlate it with the observed clinical changes. Using a intrahemispheric inhibition after stroke and to correlate it with the observed clinical changes. Using a co- registration technique, we will compare these data obtained with TMS and those obtained by neuroimaging in Project 2. This is aimed to address some of the discrepancies between these two exploratory modalities in Project 2. This is aimed to address some of the discrepancies between these two exploratory modalities in previous studies and to obtain a more comprehensive insight into cortical reorganization in the adult human brain. Our set of data will be compared to the information obtained from a primate model in Project 3 in similar study paradigms. This will allow us to obtain information on neurobiological changes associated with the reorganizational process. The ultimate aim in these studies is to determine which type of reorganization results in a positive or negative motor and rehabilitative outcome and to obtain evidence of the neurochemical process involved in order to be able to design specific pharmacological or non pharmacological therapies to enhance the recovery process after stroke.